Neuronal stimuli are transmitted by the central nervous system (CNS) through the interaction of a neurotransmitter released by a neuron, which neurotransmitter has a specific effect on a neuroreceptor of another neuron.
L-glutamic acid is considered to be the major excitatory neurotransmitter in the mammalian CNS, consequently playing a critical role in a large number of physiological processes. Glutamate-dependent stimulus receptors are divided into two main groups. The first group comprises ligand-controlled ion channels whereas the second comprises metabotropic glutamate receptors (mGluR). Metabotropic glutamate receptors are a subfamily of G-protein-coupled receptors (GPCR). There is increasing evidence for a peripheral role of both ionotropic and metabotropic glutamate receptors outside of the CNS e.g., in chronic pain states.
At present, eight different members of these mGluRs are known. On the basis of structural parameters such as sequence homology, the second messenger system utilized by these receptors and their different affinity to low-molecular weight compounds, these eight receptors can be divided into three groups: mGluR1 and mGluR5 belong to group I which couple to phospholipase C and their activation leads to intracellular calcium-ion mobilization. Both mGluR2 and mGluR3 belong to group II and mGluR4, mGluR6, mGluR7 and mGluR8 belong to group III, which couple to adenyl cyclase with their activation causing a reduction in second messenger cAMP and as such a dampening of the neuronal activity.
Group I mGluR modulators have been shown to modulate the effects of the presynaptically released neurotransmitter glutamate via postsynaptic mechanisms. Moreover, as these modulators can be both positive and/or negative Group I mGluR modulators, such modulators may increase or inhibit the effects of these metabotropic receptors. Since a variety of pathophysiological processes and disease states affecting the CNS are thought to be related to abnormal glutamate neurotransmission and group I mGluRs are shown to be expressed in several areas of the CNS, modulators of these receptors could be therapeutically beneficial in the treatment of CNS diseases.
Therefore, group I mGluR modulators may be administered to provide neuroprotection in acute and chronic pathological conditions such as: AIDS-related dementia, Alzheimer's disease, Creutzfeld-Jakob's syndrome, bovine spongiform encephalopathy (BSE) or other prion related infections, diseases involving mitochondrial dysfunction, diseases involving β-amyloid and/or tauopathy such as Down's syndrome, hepatic encephalopathy, Huntington's disease, motor neuron diseases such as amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), olivoponto-cerebellar atrophy, post-operative cognitive deficit (POCD), Parkinson's disease, Parkinson's dementia, mild cognitive impairment, dementia pugilisitca, vascular and frontal lobe dementia, cognitive impairment, eye injuries or diseases (e.g. glaucoma, retinopathy, macular degeneration), head and spinal cord injuries/trauma, hypoglycaemia, hypoxia (e.g. perinatal), ischaemia (e.g. resulting from cardiac arrest, stroke, bypass operations or transplants), convulsions, glioma and other tumours, inner ear insult (e.g. in tinnitus, sound or drug-induced), L-dopa-induced and tardive dyskinesias.
Other indications in this context include a symptomatological effect on the following conditions: addiction (nicotine, alcohol, opiate, cocaine, amphetamine obesity and others), amyotrophic lateral sclerosis (ALS), anxiety and panic disorders, attention deficit hyperactivity disorder (ADHD), restless leg syndrome and hyperactive children, autism, convulsions/epilepsy, dementia (e.g. in Alzheimer's disease, Korsakoff syndrome, vascular dementia, HIV infections), major depressive disorder or depression (including that resulting from Borna virus infection) and bipolar manic-depressive disorder, drug tolerance e.g. to opioids, movement disorders, dystonia, dyskinesia (e.g. L-Dopa-induced, tardive dyskinesia or in Huntington's disease), fragile-X syndrome, Huntington's chorea, irritable bowel syndrome (IBS), migraine, multiple sclerosis, muscle spasms, pain (chronic and acute, e.g. inflammatory pain, neuropathic pain, allodynia, hyperalgesia, nociceptive pain), Parkinson's disease, post traumatic stress disorder, schizophrenia (positive and negative symptoms), spasticity, tinnitus, Tourette's syndrome, urinary incontinence and vomiting, pruritic conditions (e.g. pruritis), sleep disorders, micturition disorders, neuromuscular disorder in the lower urinary tract, gastroesophageal reflux disease (GERD), lower esophageal sphincter (LES), functional gastrointestinal disorders, dyspepsia, regurgitation, respiratory tract infection, bulimia nervosa, chronic laryngitis, asthma (e.g. reflux-related asthma), lung disease, eating disorders, obesity and obesity-related disorders.
Yet further indications for Group I mGluR modulators include those indications wherein a particular condition does not necessarily exist but wherein a particular physiological parameter may be improved through administration of the instant compounds, for example cognitive enhancement.
Positive modulators may be particularly useful in the treatment of positive and negative symptoms in schizophrenia and cognitive deficits in various forms of dementia and mild cognitive impairment.
Among the Group I mGluR modulators, those which exhibit a modulatory effect on mGluR5 receptors and thus may affect conditions or diseases associated with the function of those mGluR5 receptors are of particular interest. In addition to the utility of mGluR5 modulators in preventing and/or treating the conditions and/or diseases mentioned above, mGluR5 positive modulators or agonists may be particularly useful for preventing and/or treating conditions or diseases that are associated with an insufficient stimulation or activity of mGluR5 receptors. mGluR5 modulators and especially mGluR5 positive modulators or agonists may be particularly useful for preventing and/or treating addiction, neuropathic pain, L-dopa-induced and tardive dyskinesias, ALS, fragile-X syndrome, Parkinson's disease, anxiety disorders, epilepsy, positive and/or negative symptoms of schizophrenia, cognitive impairment, or for cognitive enhancement and neuroprotection.